The present invention relates to a magneto-resistive composite head having a structure for evading damage of its magneto-resistive element caused by discharge current generated at read/write movement, and a magnetic disk device having the same.
Along with recent development of large capacity and high density magnetic disk devices, reproduction output of magnetic recording media becomes finer and finer, and magneto-resistive composite heads, which have advantage for detecting the fine reproduction output, are to be used widely.
In the magneto-resistive composite head, comparatively large reproduction output can be obtained making use of the magneto-resistive effect, independent of head speed relative to the recording medium.
FIG. 5 is a perspective view illustrating a conventional example of a magnetic disk device provided with magneto-resistive composite heads. The magnetic disk device comprises a magnetic recording medium (a magnetic disk) 31 rotatably supported around an axis A, a magneto-resistive composite head (hereinafter simply called the composite head) 42. The composite head 42 is unitized in a slider 12 and supported by a suspension 44 movable in a quasi-radial direction of the magnetic disk 31 for reading/writing information on a recording surface thereof. The suspension 44 is driven by an actuator 47 by way of a fixation arm 45 and a carriage 46. In the magnetic disk device of FIG. 5, a head amplifier 48 is provided at a side surface of the actuator 47 for amplifying the read/write signal.
The slider 12, the suspension 44, the actuator 47 and the magnetic disk 31 are connected electrically with each other and maintained at the same potential by way of a housing (not depicted in the drawings) whereby they are mounted and covered.
With rotation movement of the magnetic disk 31, the slider 12 moves relative to the disk surface, flying Up or sliding on the disk surface in a circumference direction thereof, and moves in the radius direction according to rotation of the carriage 46, whereby the composite head 42 is positioned on a necessary point of the disk surface for reading/writing information on the recording surface of the magnetic disk 31.
FIG. 6 is a magnified sectional view of the composite head 42 which is configured making use of a thin film forming process at a side surface of the slider 12 made of a conductive material.
Referring to FIG. 6, the composite head 42 comprises a first insulation layer 13, a first magnetic shield layer 14, a second insulation layer 16, a second magnetic shield layer 17, a magnetic pole layer 18, and a third insulation layer 19, laminated in the order from the side surface of the slider 12.
The second magnetic shield layer 17 functions as a second magnetic pole layer as well, and compose a magnetic core of the recording element of the composite head 42 together with the magnetic pole layer 18. Between the first magnetic shield layer 14 and the second magnetic shield layer 17, a magneto-resistive element (hereinafter called the MR layer) 20 is configured so as to align with a facing surface 11a of the composite head facing to the recording surface of the magnetic disk 31.
The second magnetic shield layer 17 is configured as a straight plane and the magnetic pole layer 18 is configured as a concave plane, so as to create a space between them, wherein a fourth insulation layer 21 is configured. The second magnetic shield layer 17 and the magnetic pole layer 18 are magnetoelectrically connected with each other at their upper (of the drawing) ends, and their lower ends are aligned with the facing surface 11a being separated a little so as to make a magnetic gap 23. Traversing the third and the fourth insulation layer 19 and 21, a write coil 22 is configured and the write signal flows therein. To the MR layer 20, lead patterns (not depicted in the drawings) are connected for supplying a sense current, which generates reproduction voltage to be amplified by the read/write amplifier 48 according to resistivity variation of the MR layer 20.
By supplying the write signal current to the write coil 22 of the composite head 42 thus configured, magnetic information is recorded on the magnetic disk 31 with a magnetic field generated around the magnetic gap 23, and the recorded magnetic information is reproduced by supplying the sense current to the MR layer 20 through the lead patterns.
There are magnetic recording devices employing a near-contact read/write system wherein the composite head 42 is intermittently contacting with the magnet disk 31, or a contact read/write system wherein the composite head 42 is always contacting with the magnetic disk 31. By employing these read/write systems, a space between the facing surface 11a and the magnetic disk 31 is designed as narrow as possible for enlarging magnetic field intensity to be detected by the MR layer 20.
Here, the surface of the magnetic disk 31 is usually covered with an insulation material such as a protection film or a lubricant film, and it is the same with the facing surface 11a of the composite head 42. Therefore, certain static electricity is charged between the facing surface 11a and the magnetic disk 31, due to their direct friction or their friction with air molecules flowing between them, especially in the magnetic disk devices employing the above contact or near-contact read/write systems.
The composite head 42 is flying or sliding on the magnetic disk 31 separated with a space smaller than 0.1 .mu.m. Therefore, the charged static electricity is discharged through the MR layer 20 when its potential becomes higher than a breakdown voltage of the air (about 3.5 kV/.mu.m, at 20.degree. C., 1,013 hectopascal) or of the protection/lubrication film.
The electric discharge generally occurs towards a narrowest point of the insulation space or towards a good conductor such as metallic material. Therefore, in the composite head 42 having such a structure as illustrated in FIG. 6, the static electricity is easy to be discharged through the MR layer 20 which is connected to the ground by way of a good conductor of the lead patterns.
Furthermore, thickness of the second insulation layer 16 between the MR layer 20 and the first or the second magnetic shield layer 14 or 17 is very thin and within 0.3 .mu.m, for example. Therefore, electric discharges occurring towards the first or the second magnetic insulation layer 14 or 17, or towards the magnetic pole layer 18, which is electrically connected to the second magnetic shield 17, may also cause discharge current flowing through the MR layer 20 to the ground.
Thickness of the MR layer 20 is usually within about 30 nm and width thereof is within about 2 .mu.m. Therefore, discharge current flowing in the very small cross section of the MR layer 20 may cause sufficient heat, even when its current value is small, for melting and breaking the MR layer 20, resulting in loss of the reproduction function of the composite head 42.
For preventing this damage of the reproduction head, especially of the MR layer thereof, due to the discharge current, some devices have been proposed.
In a Japanese patent application laid open as a Provisional Publication No. 63019/'97 (hereinafter called the first prior art), there is disclosed a magnetic head provided with a grounding member, or a discharge arrestor, at a position nearest to the magnetic disk, for by-passing discharge current from the magnetic disk to the ground. In an composite head disclosed in another Japanese patent application laid open as a Provisional Publication No. 73419/'95 (hereinafter called the second prior art), each one of the first and the second magnetic insulation layer 14 and 17 of FIG. 6 is so configured as to contact with each different one of the lead patterns of the MR layer 20 for preventing the discharge current flowing through the MR layer 20.
In the first prior art, the first magnetic shield layer 14 and the second magnetic shield layer 17 connected with the magnetic pole layer 18 of FIG. 6 are both electrically floating to the ground, and hence, the static electricity charged in the composite head 42 is easy to be discharged through the MR layer 20. Further, when the grounding member is not correctly positioned, discharge may occur to the MR layer 20 from the good conductors of the first magnetic shield layer 14 or the second magnetic shield layer 17 and the magnetic pole layer 18, or also direct discharge from the magnetic disk 31 to the MR layer 20 may occur depending on flying posture of the magnetic head at the CSS (Contact Start Stop) or the sliding. Still further, the grounding member is to be provided on the facing surface 11a at a position nearest to the magnetic disk 31, which means other elements including the MR layer 20 should be more separated than necessary from the magnetic disk 31, resulting in degradation of sensitivity and the resolution ability of the magnetic head.
In the second prior art, complicated film growth processes are needed for configuring each of the first and the second magnetic shield layer 14 and 17 to contact with each one of the lead patterns, resulting in a high production cost of the composite head.